1. Field of the Invention
The present invention broadly relates to a press having a plurality of working stages arranged along a straight line and, more particularly, to a transfer apparatus for successively and sequentially transferring workpieces to the working stages of the press.
2. Description of the Related Art
A conventional transfer apparatus of the kind described has a pair of feed bars which are driven by a driving unit provided at one side of the press so as to sequentially perform a series of motions including advance/return, clamp/unclamp and lift/down so that each of successive workpieces is clamped, advanced and unclamped so as to be transferred from one to the next working stage. Thus, the operation relies upon simple clamping and unclamping operation for holding and releasing the workpieces, thus offering high production efficiency. This type of transfer apparatus, however, poses a problem in that it hinders the operator's sight so as to impair visibility of the workpiece and die during press working of the workpiece. In addition, the transfer apparatus of this type hampers the efficiency of the die exchanging work.
Another known transfer apparatus employs a single transfer bar having a work clamping/unclamping unit and adapted to be driven by a driving unit provided at one side of the press so as to perform advance/return and lift/down motions, thereby sequentially transferring successive workpieces. This type of transfer apparatus, although it offers improved die visibility and higher efficiency of die exchanging work, poses another problem kin that the throughput is lowered. Namely, since the transfer bar does not move towards and away from the work, the press operation has to be suspended until the work holding device on the transfer bar is moved to a position between adjacent dies, in order to avoid interference between the work holding device and the dies.
A transfer system also has been proposed in which workpieces are successively transferred by an industrial robot which is situated in front of the press. Simultaneous transfer of a plurality of workpieces by such an industrial robot, however, requires a complicated motion to be performed by the robot and, hence, longer cycle time, as well as raised costs of installation.